Strong sales of Galaxy phones propelled Samsung's quarterly profits to a record high, but its shares dropped on the prospect that its growth will slow in an increasingly crowded smartphone market.

Samsung Electronics said July-September net profit nearly doubled to 6.56 trillion won (£3.7bn) from 3.44tn won a year earlier. Revenue for the third quarter climbed 26% to 52.2tn won.

The company's shares fell 2% in Seoul after the earnings announcement. Analysts said investors were worried the widespread adoption of smartphones in developed markets and heightened competition from rivals could squeeze profits. Samsung and Apple together account for nearly half of global smartphone sales.

The South Korean company, which raked in more than half of its profit and revenue from its mobile communications business, said its Galaxy S III and Galaxy Note II smartphones would help sustain its earnings momentum in the final quarter of the year.

Samsung also plans to act more aggressively to advance its share of the tablet PC market next year, its vice presidents Kim Hyun-joon and Robert Yi said.

"The tablet market is going through a very significant change," said Yi, Samsung's head of investor relations. The release of mini tablets that are between the size of smartphones and standard tablets could open up a new growth area next year, he said.

Apple announced a smaller and cheaper iPad earlier this week, pitting its 20cm (7.9in) iPad mini against small tablets from Amazon, Google and Samsung. Samsung launched the Galaxy Note II, an overblown smartphone with a 14cm (5.5in) screen and a digital pen, in the US market earlier this week.

A number of PC makers including Samsung launched tablet and laptop computers based on Windows 8 on Friday, as Microsoft introduced a major update to its operating system, allowing it to work on tablets and desktop computers. However, Samsung's head of investor relations said it was not clear if these new products would spur a huge increase in demand.

Operating profit surged 91% to an all-time high of 8.12tn won in the third quarter, in line with the company's preliminary results released earlier this month. Samsung is the world's largest maker of computer memory chips, mobile phones and TVs.

In the latest quarter, Samsung benefited from robust sales of its Galaxy smartphones as well as demand for high-end components for mobile devices, which offset weak global PC demand and a thin profit from its memory chip business.

Its mobile communications division, which sells the Galaxy series of smartphones and tablet computers, generated revenue of 26.3tn won.

Sales of the Galaxy S III smartphone topped 20m handsets in little more than three months after its 29 May launch. Samsung said the Galaxy Note II, the latest iteration of the Note series, is expected to exceed the 10m sales of its predecessor.

The research firm IDC said Samsung had further widened its gap with the runner-up Apple in the smartphone market. IDC said Samsung had sold 56.3m smartphones versus Apple's 26.9m iPhone sales, capturing 31.3% of the global smartphone market in the third quarter.

Kim, a vice president of Samsung's mobile communications team, said the company's smartphone sales saw "a substantial shipment growth" in China. Samsung, which is the largest smartphone seller in China according to IDC, did not disclose figures.

With the latest result, Samsung set a record-high quarterly operating profit for a fourth quarter in a row. But some analysts are sceptical whether Samsung will post another increase in profit in the final quarter of this year because of higher marketing costs.

The patent disputes between Apple and Samsung linger as another negative factor for Samsung's fourth-quarter earnings, although the company has sufficient cash reserves and earnings to cushion any impact.

Samsung is trying to reverse the decision in August of a San José jury to fine it $1bn over copying Apple's design and technology for the iPhone and the iPad. The US judge's decision may be issued as early as December.

The penalty could triple if the judge finds Samsung's act of copying was wilful. But recent developments surrounding the patent disputes between Samsung and Apple, such as the US patent office's initial ruling earlier this month to invalidate one of Apple's patents, could also scale back the penalty.